Electric squib device with insulated resistance bridge wire



May 3, 1966 M. E. GILL ETAL 3,249,047

ELECTRIC SQUIB DEVICE WITH INSULATED RESISTANCE BRIDGE WIRE Filed Sept. 11, 1964 INVENTORS.

MASON E. GILL EARL D. LANGLEY A T TOPNEV United States Patent Ofi ice 3,249,047 Patented May 3, 1966 3,249,047 ELECTRIC SQUIB DEVICE WITH INSULATED RESISTANCE BRIDGE WIRE Mason E. Gill, Dow, and Earl D. Langley, Alton, Ill.,

assignors to Olin Mathieson Chemical Corporation, a

corporation of Virginia Filed Sept. 11,1964, Ser. No. 395,802 3 Claims. (Cl. 102-28) The present invention relates to improved electric explosion initiators (sometimes referred to as electric squibs) such as are used to initiate blasting or other explosive action.

In particular the present invention relates to an electric squib device having a novel structure in the region of the resistance bridge wire.

A further [feature of the invention is the provision of a novel insulation compound useful to coat the bridge Wire.

A further feature of the invention is the provision of a novel squib device including at least two lead wires joined by a bridge wire where the bridge wire and the junction thereof with the lead wires is coated with an insulation material.

A further feature of the invention is the provision of an electric squib device which develops a resistance through the bridge wire circuit of greater than 20,000 ohms within 20 milliseconds after firing.

A further feature of the invention is the provision of a novel electric squib device susceptible of firing within two milliseconds after the application of current ranging from five-tenths (.5) to seventy-five hundredths (.75) ampere at a voltage ranging from sixty-five hundredths (.65) to nine hundred seventy-five thousandths (.975) volt, the bridge wire circuit of said squib developing a resistance greater than 20,000 ohms within 20 milliseconds after firing.

An electric squib device embracing certain principles of the present invention may comprise a pair of spaced leg posts or lead wires joined by a bridge wire, insulating coating covering the bridge wire and a bead of heat sensitive ignition material deposited on said insulation free of physical contact with said bridge wire.

An electrical insulating material embracing certain principles of the invention may comprise an insulating material having a resistivity of at least one thousand (1000) ohmscentimeters.

Other features and advantages of the present invention will become more apparent from an examination of the succeeding specification when considered in conjunction with the drawing in which:

FIG. 1 is a sectional view of an electric squib device embracing the principles of the present invention, and,

FIG. 2 is a transverse section of FIG. 1 as viewed in the plane of the line 22 and in the direction shown.

Referring now to the drawings, the reference numerals 11 and 12 designate a pair of electrical lead wires supported in a ceramic or glass insulation plug 13.

The lead wires fall flush with the right end of the plug 13 to define end faces 14 and 16.

The end faces 14 and 16 are joined as by welding or other suitable metallurgical bond with a resistance bridge wire indicated by the reference numeral 17.

The plug 13 is supported by a collar 18 in turn telescoped into a housing 19 where the housing 19 is filled with a main explosive charge indicated by the reference numeral 21.

To this point, the structure described illustrates a typical electric squib device well known to individuals skilled in the art to which the present invention pertains.

The improvement flowing from the present invention involves coating the bridge wire 17 with an electrical insulation material having a resistivity of at least one thousand (1000) ohms-centimeters.

'In some embodiments of the invention the bridge Wire alone is coated with the insulation material while in others the insulation material is coated upon the bridge wire including the junction thereof with the end faces of the lead wires as shown in FIGS. 1 and 2. The insulation material is indicated by the reference numeral 22.

A particular insulation material useful in the present invention comprises a mixture of from ninety to one hundred ten grams of Polyurethane Prepolymer, manufactured by E. I. du Pontde Nemours and sold to the trade under the name Adiprene-L, and from eight (8) to thirteen (13) grams of Methylene-Bis-(o- Chloroaniline), manufactured by E. I. du Pont de Nemours Company and sold to the trade under the name Moca.

A bead or coating of ignition material identified by the reference numeral 23 is applied to the surface of the insulation 22 so that the bridge wire 17 and the lead wires are separated from the ignition material by the intervening insulation 22.

Stated otherwise, the bead 23 of ignition material is entirely free and separate from any contact with the bridge wire and the lead wires.

The primary limitation to the ignition material 23 is that it be of heat sensitive character.

One ignition material found useful in the present invention bears the following formulation:

50 milligrams Ethyl-cellulose dissolved in 5 cc. T.X.E.B. Solution to which is added 5 grams A.O. Triple Salt (Lead Styphnate).

T.X.E.B. Solution is identified as follows:

Percent by volume Toluene 40 Xylene 35 Ethanol 15 Butanol 10 The particular advantage of the present invention is that we have found that the introduction of insulation material between the bead 23 of ignition material and the electric resistance bridge 17 including the end faces 14 and 16 of the connected lead Wires develops an electric squib structure which fires electrically within 2 milliseconds while developing a resistance at least of the order of 20,000 ohms within 20 milliseconds after electrical firing. Thus, the electric squib device of the present invention does not lay down an electrical conductive path, gaseous or solid, after firing which tends to short-circuit the squib after firing.

The squib of the present invention is particularly useful where the electrical power source actuating the squib is of limited potential and where a short circuit after firing would operate to discharge the limited power source.

It is anticipated that a wide variety of modifications and changes may be devised in the present invention without departing from the spirit and scope thereof.

What is claimed is:

1. In an electric squib device including a pair of spaced lead wires joined at their ends by a resistant bridge wire, said squib device being susceptible of electrical firing within 2 milliseconds after the application of current to said bridge wire ranging from five tenths (.5) to seventy-five hundredths (.75 amere at a voltage ranging from sixtyfive hundredths (.65) to nine hundred seventy-five thousandths (.975) volt, said squib device developing a resistance greater than 20,000 ohms within 20 milliseconds after firing, the improvement comp-rising an insulating coating covering the bridge wire and a bead of heat sensiphysical contact with the bridge wire.

2. In an electric squib device including a pair of spaced lead Wires joined at their ends by a resistant bridge Wire, said squib device being susceptible of electrical firing within 2 milliseconds after the application of current to said bridge wire ranging from five tenths (.5 to seventyfive hundredths (.75) ampere at a voltage ranging from sixty-five hundredths (.65) to nine hundred seventy-five thousandths (.975) volt, said squib device developing a resistance greater than 20,000 ohms within 20 milliseconds after firing, the improvement comprising an insulating coating covering the bridge wire and the junction of the bridge wire With the ends of said said lead wires and a bead of heat sensitive ignition material deposited on said insulation free of physical contact with all Wires.

3. In an electric squib device including a pair of spaced lead wires joined at their ends by a resistant bridge Wire, the improvement comprising an insulating coating covering the bridge wire and the junction of the bridge wire with the ends of said lead wires and a bead of heat sensitive ignition material deposited on said insulation free of physical contact With all Wires, said squib device being susceptible of electrical firing within 2 milliseconds after the application of current to said bridge wire ranging from five tenths (.5) to seventy-five hundredths (.75) ampere at a voltage ranging from sixty-five hundredths (.65) to nine hundred seventy-five thousandths (.975) volt, said squib device developing a resistance greater than 20,000

ohms Within 20 milliseconds after firing.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES The Condensed Chemical Dictionary, sixth ed., 1956.

BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL FEINBERG, Examiner.

R. V. LOTTMANN, Assistant Examiner. 

1. IN AN ELECTRIC SQUIB DEVICE INCLUDING A PAIR OF SPACED LEAD WITHIN JOINED AT THEIR ENDS BY A RESISTANT BRIDGE WIRE, SAID SQUIB DEVICE BEING SUSCEPTIBLE OF ELECTRICAL FIRING WITHIN 2 MILLISECONDS AFTER THE APPLICATION OF CURRENT TO SAID BRIDGE WIRE RANGING FROM FIVE TENTHS (.5) TO SEVENTY-FIVE HUNDREDTHS (.75) AMERE AT A VOLTAGE RANGING FROM SIXTYFIVE HUNDREDTHS (.65) TO NINE HUNDRED SEVENTY-FIVE THOUSANDTHS (.975) VOLT, SAID SQUIB DEVICE DEVELOPING A RESISTANCE GREATER THAN 20,000 OHMS WITHIN 20 MILLISECONDS AFTER FIRING, THE IMPROVEMNT COMPRISING AN INSULATING COATING COVERING THE BRIDGE WIRE AND A BEAD OF HEAT SENSITIVE IGNITION MATERIAL DEPOSITED ON SAID INSULATION FREE OF PHYSICAL CONTACT WITH THE BRIDGE WIRE. 